The present invention is directed generally to a bale tier for horizontal extrusion balers and horizontal closed chamber balers. More particularly, the invention is directed to an automatic bale tier or strapper for tying one or more wires around a bale of compacted material. Automatic balers and bale tiers are well-known in the art. For example, U.S. Pat. No. 3,528,364 discloses an automatic bale tier for an extrusion baler including a vertical column of wire transport heads, each head being provided with rollers and a "V" wire guide. See FIG. 8. The heads are driven simultaneously by a single cylinder piston. The cylinder piston extends the heads through ports in a compaction ram, from one side of the machine to an opposite side wherein rack and pinion type twisters and guillotine cutters are located. In U.S. Pat. Nos. 3,929,062 and 3,999,476, there is disclosed a baler wherein wires are separately tied, in sequence, to the same bale. The wires are fed by a vertically movable strapping mechanism 30 through vertically movable wire tracks which align with track segments in the face of the compaction ram and in a chamber discharge gate.
In a horizontal extrusion baler, such as that disclosed in U.S. Pat. No. 3,528,364, material to be compacted is fed to a hopper. A compaction ram is repeatedly reciprocated so as to compress the material into a bale. The nature of the compacting process is such that the density and dimensions of the bale are not uniform. The bale tends to be more dense along its bottom portion and less dense along its top portion. A perimeter line defined by a horizontal plane intersecting the bale tends to be shorter at the top portion of the bale and longer at the bottom portion. Where multiple wires are to be tied around the bale, a wire loop surrounding a denser portion of the bale should have a longer length than a wire loop surrounding a less dense portion of the bale.
Also, certain materials such as cardboard have greater hysteresis or memory, i.e., ability to rebound after deformation, than other materials such as paper. Bales formed from higher hysteresis materials, if tied too tightly, can exert enough pressure on a wire loop to break the loop twist joints. In comparison, bales formed of lesser hysteresis materials can be tied more tightly without danger of breakage of the loop twist joints. Thus, the lengths of the wire loops which tie or bind a bale should be variable based on the type of material from which the bale is formed.
Prior art automatic bale tiers such as that disclosed in U.S. Pat. No. 3,528,364 tie one or more wires in closed loops around the bale such that the closed loops are equal in length and do not vary from bale to bale. Accordingly, these bale tiers do not account for variations in materials, density and dimension of the bale. If the wires are tied in closed loops having identical lengths, there will either be slack in the wire loop surrounding the least dense portion of the bale in which case the wire loop may work loose from the bale, or excessive tension in the wire loop surrounding the densest portion of the bale in which case the wire loop is susceptible to breakage. Similarly, if the lengths of the wire loops do not vary from bale to bale, to account for different material properties, bales made from higher hysteresis materials may break the loop twist joints.
The problem solved by the present invention is that of automatically tying a bale with multiple wire loops having separately adjustable, pre-determined lengths to match the variations in materials, density and dimensions of the bale thereby eliminating breakage or slack in the wire loops.